Securing arrangement for reamers in raise boring

ABSTRACT

A safety arrangement which pertains to drill bits for reamer drilling and which is intended to prevent the drill bit from falling freely down the hole in the event of a breakage in an element that connects the drill bit with an overlying rotatable carrier element, the element forming part of a drill string that carries the drill bit, wherein the element includes a longitudinal hole that extends internally along at least a part of the length of the element, and the hole has disposed therein a safety device which functions to capture the element and therewith also the drill bit should the element break, the capture being achieved by virtue of the safety device being connected to a threaded part of the overlying element and also to a part of the element located at a distance from the threaded part of the element.

The present invention relates to a safety arrangement relating to drill bits for drill hole reaming or broaching, i.e. drilling of vertical holes of larger diameter from the bottom of a pre-drilled hole and upwards, with the aid of a drill bit suspended from a rod extending through said pre-drilled hole or pilot hole. Drill bits of this kind are normally referred to as reamers. The top of the rod carrying the drill bit is fastened to the drilling unit which causes the rod, and therewith the dill bit, to rotate. The drilling unit also draws the rod and the drill bit successively upwards, as the dill bit cuts away the rock around the pilot hole.

It is obvious that the equipment used in this type of drilling is subjected to high stresses and strains. A particularly sensitive point in this regard is the connection between the rod and the bit, where it is found that the stinger screwed to the rod centrally of the bit tends to fracture or break off precisely at the screw joint. These stresses are torque stresses, tension stresses and flexural stresses, which result in breaking of the stinger, particularly at its conical male thread, and therewith the loss of the bit. Such breakages can, of course, lead to serious injury of workmen in the vicinity and also serious damage to the actual bit, in addition to the work consequently involved in changing the stinger and possibly also the lower part of the rod. Other connections in the drill string are subjected to serious corresponding stresses, and if a breakage occurs in one of the connecting drill pipes or in the stabilisers, breakages are also known to occur in corresponding parts, i.e. in or adjacent to the screw thread in the joins or connections between two elements.

Accordingly, it is an object of the present invention to provide a safety device which is able to prevent the drill bit from falling freely downwards in the event of a breakage at an element that connects the bit to an overlying connected rotatable, carrying element included-in a drill string carrying the drill bit.

In accordance with the invention this object is achieved by providing said element with a hole or bore which extends along at least a part of the length of said element and which houses a safety device that functions to capture the element and therewith also the drill bit in the event of a breakage, wherein the safety device is connected to a threaded part of the overlying element and to a part of the element spaced from said threaded part thereof.

According to a preferred embodiment of the invention, the safety device has the form of a safety rod that includes a transverse member at either end thereof, said members having a length which is greater than the diameter of the hole in said element and are received in a widened portion of the hole in the proximity of said ends of the safety rod.

According to another preferred embodiment of the invention, at least one of the widened portions of the hole in said element has a given axial extension which enables the element to move axially to some extent in the event of a breakage.

The invention will now be described with reference to a non-limiting embodiment thereof, and also with reference to the accompanying drawings, in which FIG. 1 is a perspective view of a drill bit having a centrally mounted connecting element (stinger); FIG. 2 is a schematic longitudinal view of a first embodiment of a stinger that includes an inventive safety device; and-FIG. 3 is a view corresponding to FIG. 2 of a second exemplifying embodiment.

FIG. 1 illustrates a drill bit 1 that comprises a number of cutters 2 and a connecting element in the form of a stinger 3 mounted centrally of the bit 1. The stinger 3 has at its upper end an external screw thread 4 by means of which the drill bit 1 can be connected to a downwardly extending drill string (not shown) that includes further connecting elements. The drill string enables the drill bit 1 to be rotated and drawn upwards so that the cutters 2 on the top of the drill bit will cut away the rock around the pilot hole in which the drill string extends and in which the stinger is located. Removal of the rock places the screw joint between the stinger 3 and the next overlying element in the drill string to a great deal of stress, due to the torque, tensile and bending loads that act simultaneously thereon. It has been found that a breakage is more likely to occur at the upper part of the stinger 3. In the event of a breakage, the upper threaded part of the stinger 3 will normally remain attached to the lower thread connection of the element that lies immediately above the connection, whereas the actual drill bit 1 and the remainder of the stinger 3 will fall down to the bottom of the pre-drilled hole.

FIG. 2 illustrates an exemplifying embodiment of a stinger 3 provided with a safety device according to the present invention. In this case the safety device comprises a safety rod 5 that extends through a longitudinal hole 6 provided in the stinger 3. In the illustrated case the hole 6 extends essentially through the full length of the stinger, with a minimum requirement that the length of the hole is such as to extend at least beyond the region where breakage of the stinger is normally expected to occur. The hole 6 has in its upper end in the threaded portion of the stinger 3 a radial widening 7 and a radial widening 8 at its other end.

The safety rod 5 has at each end a respective flange 9, 10 which projects radially outwards from the rod 5 and which has a diameter that is larger than the diameter of the hole 6 that extends through the rod 5, so as to prevent the rod from being drawn through the hole. It will be understood, however, that the flange may be substituted with some other transverse member whose length is greater than the diameter of the longitudinally extending hole 6. Should the stinger 3 break, the safety rod will hold up the broken part of the stinger 3, and therewith also the drill bit 1, by virtue of the engagement of the flanges 9, 10 with the surfaces of the widened portions 7, 8 of said hole 6. A break does not normally occur at the very uppermost part of the stinger 3, where the hole widening 7 is situated, but slightly beneath this point, and hence the safety rod 5 will be held firmly in the upper widened portion 7 of the hole and the lower flange 10 on the rod 5 will support the stinger and the drill bit by virtue of its abutment with the surfaces of the widened portion 8 of said hole.

FIG. 3 illustrates a variant of the embodiment shown in FIG. 2 which differs from what is shown in FIG. 2 and from what has been described with reference thereto by the fact that the lower widened portion 8′ of the hole in the stinger 3 has a longer axial length and that, in a normal state, the flange 10 on the safety rod 5 is located at a given distance from the bottom of the widened portion 8′ as shown in the Figure. With this embodiment there is obtained a more distinct axial displacement of the drill bit 1 from the rod, which is connected to the drilling unit, whereby the drill bit will move out of contact with the rock face. This will indicate immediately that a break has occurred, because of the ensuing sudden lack of resistance against rotation of the drill bit.

It will be understood that the safety device is not restricted to a rod that extends through the greater part of the length of the stinger/element and that some other means can be used instead, such as a wire that is able to support the weight of the drill bit should the stinger/element break. The safety arrangement according to the invention will preferably be constructed so that the longitudinal holes in respective elements can be through-passed by a rinsing or flushing medium, such as water. In this case it is necessary to dimension the safety device so that the flushing or rinsing medium is able to pass through the longitudinal channels. The transverse member described above should also be designed to allow said medium to pass said member. This should present no problem when said transverse member is rod shaped. When the transverse member is a flange, the flange may conveniently be perforated with axially extending passageways.

Although the invention has been described by way of an embodiment in which the element is a stinger, it will readily be understood that a corresponding arrangement can be provided in other elements included in the drill string, such as connecting drill pipes and stabilisers. These elements also include screw threads corresponding to those described above with regard to the stinger and are liable to break at corresponding places. Thus, other elements in the drill string can be made safe against the event of a breakage by means of the inventive arrangement, so that a breakage in their connection with another element need not result in the loss of the drill bit and that part of the drill string that lies beneath the place at which the breakage occurred. 

1. A safety arrangement pertaining to drill bits for reamer drilling that is intended to prevent the drill bit (1) from falling freely down the hole in the event of a breakage in an element (3) that connects the drill bit (1) with an overlying rotatable carrier element, said element forming part of a drill string that carries the drill bit (1), characterised in that the element (3) includes a longitudinal hole (6) that extends internally along at least a part of the length of said element (3), and wherein the hole has disposed therein a safety device (5) which functions to capture the element and therewith also the drill bit (1) should the element (3) break, said capture being achieved by virtue of the safety device (5) being connected to a threaded part (4) of the overlying element (3) and also to a part of said element (3) located at a distance from said threaded part (4) of the element.
 2. A safety arrangement according to claim 1, characterised in that the safety device (5) has the form of a safety rod (5) which has a respective transverse member (9, 10) at each of its ends, wherein said transverse members (9, 10) have a length that is greater than the diameter of the hole (6) in the element (3) and are accommodated in respective widened portions (7, 8; 7, 8′) of the hole (6) in the proximity of respective ends of the safety rod (5).
 3. A safety arrangement according to claim 2, characterised in that at least one of the widened portions (8′) of the hole (6) in the element (3) has a given extension axially, so that the element (3) can move slightly in an axial direction in the event of a breakage.
 4. A safety arrangement according to claim 2, characterised in that the transverse element (9, 10) is a flange that projects outwardly from the safety rod.
 5. A safety arrangement according to claim 1, characterised in that the element (3) is the stinger (3) that is connected directly to the drill bit (1).
 6. A safety arrangement according to claim 1, characterised in that said element is a stabiliser included in the drill string.
 7. A safety arrangement according to claim 1, characterised in that said element is a connecting drill pipe included in the drill string.
 8. A safety arrangement according to claim 3, characterised in that the transverse element (9, 10) is a flange that projects outwardly from the safety rod.
 9. A safety arrangement according to claim 2, characterised in that the element (3) is the stinger (3) that is connected directly to the drill bit (1).
 10. A safety arrangement according to claim 3, characterised in that the element (3) is the stinger (3) that is connected directly to the drill bit (1).
 11. A safety arrangement according to claim 4, characterised in that the element (3) is the stinger (3) that is connected directly to the drill bit (1).
 12. A safety arrangement according to claim 8, characterised in that the element (3) is the stinger (3) that is connected directly to the drill bit (1). 